Catalysts for preparation of synthetic rubber



Patented Oct. 24, 1950 CATALYSTS FOR PREPARATION OF SYNTHETIC RUBBERRobert W. Brown, Naugatuck, Conn., assignor to 7 United States RubberCompany, New York, N. Y., a corporation of New Jersey No Drawing.Original application August 27,

1948, Serial No. 46,550. Divided and this application March 15, 1949,Serial No. 81,636

Claims.

The present invention relates to new catalysts for the preparation ofsynthetic rubber latices by the aqueous emulsion polymerization ofbutadiene-1,3hydrocarbons and mixtures of butadiene-l,3hydrocarbons withcompounds which are copolymerizable therewith.

This is a division of my co-pending application Serial No. $6,550, filedAugust 27, 1948, now abandoned.

I have found that unsubstituted and substituted arylazo aryl sulfonesare effective catalysts, or so-called initiators, in the preparation ofsynthetic rubbers by aqueous emulsion polymerization of the syntheticrubber-forming monomers. These arylazo aryl sulfones are characterizedby the structure Ar-N=NSO2-Ar. where Ar and Ar are-unsubstituted andsubstituted aryl groups. p

The arylazo arylsulfone catalysts of the present invention are fasteracting than conventional peroxidic catalysts in low temperaturepolymerizations. They have an advantage over arylazo aryl sulfides(ArN=N-S--Ar', where Ar and Ar are aryl groups), or so-called aromaticdiazo thio ethers, in that the arylazo aryl sulfides on decomposition inthe latex give rise to'thiophenols which act as regulators for thepolymer chains in the emulsion polymerization, whereas the arylazo arylsulfones of the present invention do not. Because of this, the arylazoaryl sulfides, as distinguished from the arylazo aryl sulfones of thepresent invention, combine the properties of a catalyst and a regulator,which is undesirable where the polymerization is to be regulated solelyby regulators specifically added for the purpose.

The aryl groups in the arylazo aryl sulfones of the present inventionmay have benzene nuclei or condensed benzene (e. g. naphthalene) nuclei,and may be unsubstituted or have substituents which are essentiallyunreactive in character and which therefore do not interfere with thepolymerization, such as 'alkyl, alkoxy, halo and sulfo substituents asin alkarylle. g. o-tol'yl, and

2,4-dimethylphenyl), alkoxyaryl(e. g; 4-methoxyphenyl and4-ethoxyphenyl), haloaryl (e. g. 4-chlorophenyl and 4-bromophenyl)andsulfoaryl -(e. g. 4-su1fophenyl)-radicals. The term aryl as usedherein, where it is not otherwise defined, is .used in its accepted-meaning as an organic radical derived from an aromatic -hydr0- carbonby the removal of one hydrogen atom, e. g. phenyl, naphthyl, tolyl,dimethylphenyl'- The, arylazo aryl sulfones of the present invention maybe prepared by the reaction of a substituted or unsubstituted aryldiazonium halide (prepared by diazotizing an aromatic amine) with thealkali-metal (usually sodium) salt of a substituted or unsubstitutedaryl sulfinic acid according to the equation:

Ar-'N=N-Cl+NaSOzAr- AIN=NSOz-AI"+N8.C1 Illustrative examples of thedetailed preparation of a representative number of arylazo aryl sulfonesthat are used as catalysts in the manufacture of synthetic rubber latexaccording to the present invention are set forth in Examples I to XIIIbelow.

EXAMPLE I 2,4-dimethylpheny Zazo p-tolyl sulfone Six and one tenth g.(0.05 mol) of l-amino- 2,4-dimethyl benzene was diazotized at 0-10 C. inaqueous hydrochloric acid solution with a slight excess of sodiumnitrite. At the end of one hour excess nitrite was destroyed by additionof sulfamic acid. The resulting solution of 2,4-

dimethylphenyl diazonium chloride was thenadded slowly with vigorousmechanical stirring to a cold solution of 15 g. of the sodium salt ofp-tolyl sulfinic acid (dihydrate) and 10 g. of

sodium carbonate in 200 m1. of water. The yellow suspension was stirredfor a few minutes, then placed in the refrigerator over night. The nextday the solid was filtered off and Washed with water. It was thendissolved in ml. of diethyl ether, the solution was decanted from alittle EXAMPLE II Phenyldeo p-tolylsulfone Four and six-tenths g. (0.05mol) .of aniline was trite. At the end of acetate and added slowly withvigorous mechanamas ical stirring to acold solution of 9.7 g. of thesodium salt of p-tolyl sulfinic acid (dihydrate) in 200 ml. of water.The resulting yellow suspension was stirred for a few minutes afterwhich the solid was filtered oil and washed with water. A sample of theproduct was dissolved in 25 ml. of ether. The solution was dried withmagnesium sulfate and an equal volume of petroleum ether added. Bluntyellow needles began to separate at once. The mixture was placed in therefrigerator until thoroughly cooled; the product was then filtered oiland washed with petroleum ether. The melting point of the purifiedphenylazo p-tolyl sulione was 90-92 0.

EXAMPLE HI 4-methoryphenylazo p-tolyl suljonc Three and one tenth g.(0.025 moi.) of 1- amino-4-methoxy benzene was diazotized at -10 C. inaqueous hydrochloric acid with a slight excess of sodium nitrite. At theend of one hour excess nitrite was destroyed by addition of sulfamicacid. The resulting solution of 4-methoxy benzene diazonium chloride wasthen neutralized to Congo red paper with potassium acetate and addedwith vigorous mechanical stirring to a cold solution of 5.3 g. of thesodium salt of p-tolyl sulfinic acid (dihydrate) in 100 ml. of water.After about two hours in the ice bath the yellow solid was filtered oiland washed with water. A sample of the product was dissolved in 25 ml.of ether. The solution was dried with magnesium sulfate and .an equalvolume of petroleum ether added. The mixture was placed in therefrigerator until thoroughly cooled; the yellow crystals whichseparated were then filtered off and washed with petroleum ether. Themelting point of the purified 4- methoxyphenylazo p-tolyl sulione was94-95" C.

EXAMPLE IV I-naphthylazo p-tolyl sulfone Five g. (0.035 mol) of alphanaphthyl amine was diazotized at 0-10 C. in aqueous hydrochloric acidsolution with a slight excess oi sodium nitrite. At the end of one hourexcess nitrite was destroyed by addition of sulfamic acid. The resultingsolution of alpha naphthalene diazonium chloride was neutralized toCongo red paper with sodium acetate and added slowly with vigorousmechanical stirring to a cold solution of 8.0 g. (0.037 mol) of thesodium salt of p-tolyl sulfinic acid (dihydrate) in 200 ml. of water.The resulting yellow suspension was stirred for a few minutes; then theyellow solid was filtered oil? and washed with water. The product waspurified by solution in benzene and precipitation with petroleum ether.The melting point of the purified l-naphthylazo p-tolyl sulrone was102-103 C.

EXAMPLE V Z-naphthylazo p-toly1 suljone Five g. (0.035 mol) of betanaphthyl amine was diazotized at 0-10" C. in aqueous hydrochloric acidsolution with a slight excess of sodium nitrite. At the end of one hourexcess nitrite was destroyed by addition of sulfamic acid. The resultingsolution of beta naphthalene diazonium chloride was neutralized to Congored paper with sodium acetate and added slowly with vigorous mechanicalstirring to a cold solution of 8.0 g. (0.037 mol) of the sodium salt ofp-tolyl sulfinic acid (dihydrate) in 200 ml. of water. The I- 4 suitingsuspension was stirred for a few minutes, then the yellow solid wasfiltered oii and washed with water. The product was purified by solutionin benzene and precipitation with petroleum ether. The melting point ofthe purified 2- naphthylazo p-tolyl sulione was 112-114 C.

EXAMPLE VI 4-sulfophenylazo p-tolyl suljone sodium salt Four and threetenths g. (0.025 mol) of sulranilic acid was dissolved in a solution of1.8 g. of sodium carbonate in 70 ml. of water. A solution of 1.72 g. orsodium nitrite in a little water was then added. The resulting solutionwas cooled and poured into a mixture of 6 m1. of hydrochloric acid and50 g. of ice. At the end of one half hour excess nitrite was destroyedwith sulfamic acid and the suspension of diazonium salt was poured intoa cold solution of 5.45 g. (0.025 mol) of the sodium salt of p-tolylsulfinic acid (dihydrate) in ml. of water plus 10 ml. of 10% sodiumhydroxide solution. The clear solution was stirred for a few minutes,acidified to Congo red paper with hydrochloric acid and 20 g. of sodiumchloride was added to salt out the product. The precipitated solid wasfiltered off and washed with petroleum ether. The purified yellowcrystals did not melt but decomposed on strong heating, leaving anon-volatile residue.

EXAMPLE VII Phenylazo Z-naphthyl suljone Two g. (0.02 mol) of anilinewas diazotized at 0-10 C. in aqueous hydrochloric acid solution with aslight excess of sodium nitrite. At the end of one hour excess nitritewas destroyed by addition of sulfamic acid. The resulting solution ofbenzene diazonium chloride was neutralized to Congo red paper withsodium acetate, and to it was added with vigorous stirring a solution014.3 g. (0.02 mol) of the sodium salt of beta naphthalene sulfinic acidin 100 ml. of water. A yellow oil separated at once. The mixture wasstirred in a bath for one hour, then stored in the refrigerator for anhour. The water was decanted from the oil and the latter was taken up indiethyl ether. It crystallized at once on contact with the ether. Thesolution was dried over magnesium sulfate, filtered and cooled to 'l0 C.The bright yellow crystals were filtered ofl and dried under vacuum. Themelting point of the purified phenylazo z-naphthyl sulfone was 86-8'1 C.

EXAMPLE VIlI 4-methomyphenylazo Z-naphthyl sulfone Three g. (0.024 mol)of 4-methoxy-l-amino benzene was diazotized at 0-10 C. in aqueoushydrochloric acid solution with a. slight excess of sodium nitrite. Atthe end of one hour excess nitrite was destroyed by addition of sulfamicacid. The resulting solution of 4-methoxy benzene diazonium chloride wasneutralized to Congo red paper with sodium acetate and to it was addedwith vigorous stirring a solution or 5.2 g. (0.024 mol) of the sodiumsalt of beta naphthalene sulfinic acid in 100 ml. of water. After onehour of stirring in the ice bath the semi-solid product was filteredoff. It crystallized on treatment with diethyl ether. The crystals weredissolved in diethyl ether; the solution was dried and filtered. The drysolution was diluted with its volume of petroleum ether and cooled to-70 C. The yellow crystals were filtered off and dried under vacuum. Themelting point of the purified 4- amas methoxyphenylazo 2-naphthylsulfone was 94 to 95 C.

Examples of other arylazo aryl sulfones that may be used as catalysts inthe emulsion polymerization of synthetic rubbers and that are madesimilarly to the above by reacting the selected aryl diazonium chloridewith the sodium salt of the selected aryl sulflnic acid' are phenylazophenyl sulfone, o-tolylazo phenyl sulfone, p-tolylazo phenyl sulfone,o-methoxy phenylazo phenyl sulfone, p-methoxy phenylazo phenyl sulfone,2,4-dimethyl phenylazo phenyl sulfone, 2,5- dimethyl phenylazo phenylsulfone, o-chlorophenylazo phenyl sulfone, m-chlo'rophenylazo phenylsulfone, p-chlorophenylazo phenyl sulfone, o-phenyl phenylazo phenylsulfone, p-phenyl phenylazo phenyl sulfone, 2-sulfo-phenylazo phenylsulfone-sodium salt, phenylazo o-tolyl sulfone, phenylazo 2,5-dimethylphenyl sulfone, phenylazo 2-chloro phenyl sulfone, 4-sulfo naphthylazophenyl sulfone-sodium salt, 5-su1fo l-naphthylazo phenyl sulfone-sodiumsalt, 6- sulfo 2-naphthylazo phenyl sulfone-sodium salt.

The arylazo aryl sulfone catalysts may be used in the preparation ofvarious synthetic rubber latices made by the emulsion P lymerization ofpolymerizable material by incorporating the catalyst in the aqueousemulsion of 'polymerlzable monomers in the usual manner beforepolymerization. The amount of arylazo aryl sulfone used may be from 0,01to 0.5 part by weight per 100 parts of polymerizable monomers in theemulsion. The polymeriztble monomers may be emulsified win the water byany of the emulsifying agents usually employed. such as sodium soaps ofhigher fatty acids and rosin acids, or other surfaceactive agents (e. g.alkali-metal salts of alkylated naphthalene sulfonic acid or fattyalcohol sulfates), and the temperature for the polymerization may be anydesired temperature as from 10 to 65 C. The emulsion of polymerizablemonomers may contain a conventional regulator such as a higher alkylmercaptan or an aromatic mercaptan. The polymerizable monomers for thepreparation of the synthetic rubber may be one or a mixture ofbutadiene-l,3-hydrocarbons, for example, butadiene -1,3,2methyl-butadiene ,3 (isoprene), piperylene, 2,3-dimethylbutadiene- 1,3.The polymerizable material as is known may be a mixture of one or moreof such butadiene- ,3 hydrocarbons with one or more other polymerizablecompounds which are capable of forming rubbery copolymers withbutadiene-1,3 hydrocarbons, for example, up to 70% of such mixture ofone or more compounds which contain a 6 EXAMPLE The following formulawas loaded into four 24 ounce crown cap bottles:

Parts Butadiene '12 Styrene 28 2,4-dimethylphenylazo p-tolyl sulfone-0.06 Soap 5 Regulator 0.35 Sodium sulfate 0.3 Water 180 The soap(emulsifier) and regulator in the above formulation and in the followingexamples were those conventionally used in synthetic rubber manufacture,viz., sodium soap of dehydrogenated rosin acids, and dodecyl mercaptanregulator, respectively. The sodium sulfate was included to decrease theviscosity of the latex.

The loaded bottles were placed on a wheel polymerizer at 45 C. andagitated for 23 hours. At the end of that time 82% of the monomers hadbeen converted to polymer. The latices were blended and the polymerisolated by known coagulation with sodium chloride and dilute sulfuricacid.

The polymer was compounded in a tread stock and cured for 60 minutes at45 pounds of steam pressure. The thus cured stock, and a cured stock ofsimilar composition prepared from a synthetic 1 rubber made withpotassium persulfate catalyst single CH=C group where at least one ofthe disconnected valences is attached to an electro- 'negative group,that is, a group which substantially increases the electricaldissymmetry or polar character of the molecule, such group being otherthan H or CH3. Examples of compounds which contain a CH2=C group and arecopolymerizable with butadienes-l,3 are aryl olefins, such as styrene,and vinyl naphthalene; the alpha methylene carboxylic acids, and theiresters, nitrlles and amides, such as acrylic acid, methyl acrylate,methyl methacrylate, acrylonitrile,

(GR-S Control) had the following properties:

EXAMPLE X The following formula was loaded into a 24 ounce crown capbottle:

Butadiene '15 Styrene 25 Phenylazo p-tolyl sulfone 0.05 Soap 5.0Regulator 0.35 Sodium sulfate s 0.30 Water 180 The loaded bottle wasplaced on a wheel polymerizer in a water bath at 45 and agitated for 29.hours. At the end of this time 82% of the monomers had been converted torubbery polymer which was" isolated from the latex by known methods.

vEXAMPLEXI The following formula was loaded into a 24 ounce crown capbottle:.

' .Butadiene Styrene 25 v 4-methoxyphenylazo p-tolyl sulfone 0.05 Soap5.0

Regulator 0.35 Sodium sulfate- 0.30 Water The loaded bottle was placedon a wheel polymerizer in a water bath at 45 and agitated for 75 29hours. At the end of this time 77% of the monomers had been converted torubbery polymer which was. isolated from the latex by known methods.

. EXAMPLE XII The following formula was loaded into a 24 ounce crown capbottle:

Butadiene 75 Styrene 25 4-methoxyphenylazo 2-naphthyl sulfone- 0.05 SoapRegular 0.35 Sodium sulfate 0.30 Water 180 The loaded bottle was placedon a wheel polymerizer in a water bath at 45 and agitated for 29 hours.At the end of this time 77% of the monomers had been converted torubbery polymer which was isolated from the latex by known methods.

EXAMPLE XIII The following formula was loaded into a 24 ounce crown capbottle:

Butadiene "l5 Styrene 25 4-sulfophenylazo p-tolyl sulfone, sodium salt0.30

Soap 5 Regulator 0.35 Sodium sulfate 0.30

Water 180 The loaded bottle was placed on a wheel polymerizer in a waterbath at 45 and agitated for 23 hours. At the end of this time 57% of themonomers had been converted to rubbery polymer which was isolated fromthe latex by known means.

Examples IX to XIII above show for convenience the preparation ofbutadiene-styrene synthetic rubbers, which are the commonest commercialtype of synthetic rubber. Similar results are obtained when using thearylazo aryl sulfone catalyzers of the present invention in thepolymerization of other types of synthetic rubbers, e. g., in theemulsion polymerization polyisoprene, and of polybutadiene, and in theaqueous emulsion polymerization of monomer mixtures, such as: 75 partsof butadiene-L3 and 25 parts of methyl acrylate; 35 parts ofbutadiene-l,3, 35 parts of isoprene and 30 parts of methyl acrylate; '70parts of butadiene-L3, 25 parts of styrene and 5 parts of methylmethacrylate; 35 parts of butadiene- 1,3, 35 parts of isoprene, 25 partsof styrene and 5 parts of methyl methacrylate.

In view of the many changes and modifications that may be made withoutdeparting from the principles underlying the invention, reference shouldbe made to the appended claims for an understanding of the scope of theprotection afforded the invention.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. In a process of polymerizing in aqueous emulsion material selectedfrom the group consisting of butadiene-1,3 hydrocarbons and mixtures ofbutadiene-1.3 hydrocarbons with compounds which contain a single CH2=Cgroup and are copolymerizable therewith, the step of carrying out thepolymerization in the presence of 0.01 to 0.5 part by weight per 100parts by weight of polymerizable monomeric material of a sulfoneselected from the group consisting of unsubstituted arylazo arylsulfones and arylazo aryl sulfones in which at least one of the arylgroups is substituted by material selected from the group consisting ofalkyl, alkoxy, halo and sulfo substituents.

2. In a process of polymerizing in aqueous emulsion a mixture of abutadiene-1,3 hydrocarbon and a compound which contains a single CH2=Cgroup and is copolymerizable therewith, the step of carrying out thepolymerization in the presence of 0.01 to 0.5 part by weight per partsby weight of polymerizable monomeric material of a sulfone selected fromthe group consisting of unsubstituted arylazo aryl sulfones and arylazoaryl sulfones in which at least one of the aryl groups is substituted bymaterial selected from the group consisting of alkyl, alkoxy, halo andsulfo substituents.

3. In a process of polymerizing in aqueous emulsion a mixture ofbutadiene-1,3 and styrene, the step of carrying out the polymerizationin the presence of 0.01 to 0.5 part by weight per 100 parts by weight ofpolymerizable monomeric material of a sulfone selected from the groupconsisting of unsubstituted arylazo aryl sulfones and arylazo arylsulfones in which at least one of the aryl groups is substituted bymaterial selected from the group consisting of alkyl, alkoxy, halo andsulfo substituents.

4:. In a process of polymerizing in aqueous emulsion material selectedfrom the group consisting of butadiene-1,3 hydrocarbons and mixtures ofbutadiene-1,3 hydrocarbons with compounds which contain a single CH2=Cgroup and are copolymerizable therewith, the step of carrying out thepolymerization in the presence of 0.01 to 0.5 part by weight of aphenylazo aryl sulfone per 100 parts by weight of polymerizablemonomeric material.

5. In a process of polymerizing in aqueous emulsion a mixture ofbutadiene-1,3 and styrene, the step of'carrying out the polymerizationin the presence of 0.01 to 0.5 part by weight of a phenylazo arylsulfone per 100 parts by weight of polymerizable monomeric material.

6. In a process of polymerizing in aqueous emulsion material selectedfrom the group consisting of butadiene-l,3 hydrocarbons and mixtures ofbutadiene-1,3 hydrocarbons with compounds which contain a single CH2=Cgroup and are copolymerizable therewith, the step of carrying out thepolymerization in the presence of 0.01 to 0.5 part by weight of aphenylazo p-tolyl sulfone per 100 parts by weight of polymerizablemonomeric material.

7. In a process of polymerizing in aqueous emulsion a mixture ofbutadiene-1,3 and styrene, the step of carrying out the polymerizationin the presence of 0.01 to 0.5 part by weight of a phenylazo p-tolylsulfone per 100 parts by weight of polymerizable monomeric material.

8. In a process of polymerizing in aqueous emulsion material selectedfrom the group consisting of butadiene-1,3 hydrocarbons and mixtures ofbutadiene-1,3 hydrocarbons with compounds which contain a single CH2=Cgroup and are copolymerizable therewith, the step of carrying out thepolymerization in the presence of 0.01 to 0.5 part by weight of asulfophenylazo aryl sulfone per 100 parts by weight of polymerizablemonomeric material.

9. In a process of polymerizing in aqueous emulsion a mixture ofbutadiene-1,3 and styrene, the step of carrying out the polymerizationin the presence of 0.01 to 0.5 part by weight of a aaemes sulfophenylazoaryl sulfone per 100 parts by weight of polymerizable monomericmaterial.

10. In a process of polymerizing in aqueous emulsion material selectedfrom the group consisting of butadiene-L3 hydrocarbons and mixtures ofbutadiene-1,3 hydrocarbons with compounds which contain a single CH2=Cgroup and are copolymerizable therewith, the step of carrying out thepolymerization in the presence of 0.01 to 0.5 part by weight of analkylphenylazo aryl sulfone per 100 parts by weight of polymerizablemonomeric material.

11. In a process of polymerizing in aqueous emulsion a mixture ofbutadiene-1,3 and styrene, the step of carrying out the polymerizationin the presence of 0.01 to 0.5 part by weight of an alkylphenylazo arylsulfone per 100 parts by weight of polymerizable monomeric material.

12. In a process of polymerizing in aqueous emulsion material selectedfrom the group consisting of butadiene-1,3 hydrocarbons and mixtures ofbutadiene-1,3 hydrocarbons with compounds which contain a single CH2=Cgroup and are copolymerizable therewith, the step of carrying out thepolymerization'in the presence of 0.01 to 0.5 part by weight of analkoxyph'enylazo aryl sulfone per 100 parts by weight of polymerizablemonomeric material.

13. In a process or polymerizing in aqueous emulsion a mixture ofbutadiene-l,3 and styrene, the step of carrying out the polymerizationin the presence of 0.01 to 0.5 part by weight of an alkoxyphenylazo arylsulfone per 100 parts by weight of polymerizable monomeric material.

14. In a process of polymerizing in aqueous emulsion material selectedfrom the group consisting of butadiene-l,3 hydrocarbons and mix tures ofbutadiene-1,3 hydrocarbons with compounds which contain a single CH2=Cgroup and are copoiymerizable therewith, the step of carrying out thepolymerization in the presence of 0.01 to 0.5 part by weight of ahalophenylazo aryl sulfone per 100 parts by weight of polymerizablemonomeric material.

15. In a process of polymerizing in aqueous emulsion a mixture ofbutadiene-1,3 and styrene, the step of carrying out the polymerizat onin the presence of 0.01 to 0.5 part by weight of a halophenylazo arylsulfone per 100 parts by weight of polymerizable monomeric material.

ROBERT w. BROWN.

No references cited.

1. IN A PROCESS OF POLYMERIZING IN AQUEOUS EMULSION MATERIAL SELECTEDFROM THE GROUP CONSISTING OF BUTADIENE-1,3 HYDROCARBONS AND MIXTURES OFBUTADIENE-1,3 HYDROCARBONS WITH COMPOUNDS WHICH CONTAIN A SINGLE CH2=C<GROUP AND ARE COPOLYMERIZABLE THEREWITH, THE STEP OF CARRYING OUT THEPOLYMERIZATION IN THE PRESENCE OF 0.01 TO 0.5 PART BY WEIGHT PER 100PARTS BY WEIGHT OF POLYMERIZABLE MONOMERIC MATERIAL OF A SULFONESELECTED FROM THE GROUP CONSISTING OF UNSUBSTITUTED ARYLAZO ARYL SUFONESAND ARYLAZO ARYL SULFONES IN WHICH AT LEAST ONE OF THE ARYL GROUPS ISSUBSTITUTED BY MATERIAL SELECTED FROM THE GROUP CONSISTING OF ALKYL,ALKOXY, HALO AND SULFO SUBSTITUENTS.